Vehicle fuel economy may be improved by selectively stopping and starting the engine of a vehicle. The engine may be stopped while the vehicle is in heavy stop-and-go traffic or at stop lights, for example. Recently such engine operation has been proposed for engines coupled to automatic transmissions. However, stopping and restarting an engine may be challenging for engines coupled to an automatic transmission because of characteristics of a torque converter that may be placed between the engine crankshaft output and the transmission input. Specifically, torque converter output torque increases more rapidly as engine speed exceeds a threshold speed. If an engine is restarted and allowed to exceed the threshold speed, an increasing amount of engine torque can be transferred to the vehicle driveline and wheels. As a result, it may be possible to impart more torque from the engine to the vehicle wheels during an engine restart than is desired.
At some engine operating conditions torque converter output can be controlled by adjusting engine speed. Engine speed may be controlled by retarding and/or advancing spark delivered to engine cylinders. Further, under some engine operating conditions it may be possible to control engine speed by controlling the engine air-fuel mixture from which engine torque is generated. However, there may be engine operating conditions when engine cylinders are restricted to a threshold indicated mean effective pressure (IMEP) to consistently operate engine cylinders. For example, some fuel injectors require a minimum pulse width in order to inject an expected amount of fuel to a cylinder of the engine. If the injector is operated at a smaller pulse width, the engine cylinder may not receive fuel or the amount of fuel received may not be sufficient to support combustion in the cylinder. On the other hand, if the fuel injector is operated at the minimum pulse width, cylinder pressure may exceed a desired IMEP value. As a result, the engine may accelerate above the engine speed where an increased amount of engine torque may be transferred through the torque converter and to the vehicle wheels during an engine start while the transmission is in gear. Consequently, it may be difficult under some conditions to control engine speed during an engine start so that engine speed does not exceed a threshold level and cause the torque converter to transfer an undesirable amount of engine torque to the vehicle wheels.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for improving engine starting. One embodiment of the present description includes a method for starting an engine, comprising: stopping the engine; automatically initiating an engine restart and initiating combustion in a first cylinder of the engine; and skipping combustion, according to an order of combustion of the engine, in at least one cylinder of the engine during the engine restart after initiating combustion in the first cylinder.
By skipping a combustion event during the restart of an engine that is coupled to an automatic transmission and started in gear, it may be possible to control engine speed so that an undesirable amount of engine torque is not transferred to the wheels of a vehicle. For example, during an engine restart, combustion may be initiated in a cylinder. Combustion may proceed in other engine cylinders according to the engine combustion order (e.g., 1-3-4-2 for a four-stroke four cycle engine). However, combustion in one or more cylinders according to the combustion order may be inhibited so that engine speed approaches a desired level. In one example, combustion may be initiated in a particular cylinder of an engine. The next cylinder in the combustion order may also combust an air-fuel mixture while the third cylinder according to the engine combustion order proceeds through a cylinder cycle without combustion an air-fuel mixture. In this way, it may be possible to control engine speed and the transfer of torque from an engine to vehicle wheels during a start of an engine coupled to an automatic transmission that is in gear.
The present description may provide several advantages. In particular, the approach may reduce the possibility of transferring an undesirable amount of engine torque to vehicle wheels during an engine start. Further, the approach may improve engine speed control during engine starting irrespective of the type of transmission coupled to the engine. Further still, the approach may be able to compensate for engine hardware that may require a cylinder IMEP that is higher than is desirable during an engine start.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.